1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling hybrid automatic repeat request (HARQ) resource in a time-division duplexing (TDD) and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (CoMP), UL multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Different from the LTE/LTE-A system with frequency-division duplexing (FDD), directions of subframes of a frequency band in the LTE/LTE-A system with time-division duplexing (TDD) may be different. That is, the subframes in the same frequency band are divided into uplink (UL) subframes, downlink (DL) subframes and special subframes according to the UL/DL configuration specified in the 3GPP standard.
Please refer to FIG. 1 which is a table 10 of the UL/DL configuration with subframes and corresponding directions. In FIG. 1, 7 UL/DL configurations are shown, wherein each of the UL/DL configurations indicates a set of directions for 10 subframes, respectively. In detail, “U” means that the subframe is a UL subframe where UL data is transmitted, and “D” means that the subframe is a DL subframe where DL data is transmitted. “S” means that the subframe is a special subframe where control information and maybe data (according to the special subframe configuration) is transmitted, and the special subframe can also be seen as the DL subframe in the present invention.
Furthermore, a UL/DL configuration of a legacy UE can be changed according to system information (e.g., System Information Block Type 1 (SIB1)) transmitted by an eNB, e.g., from the UL/DL configuration 1 to the UL/DL configuration 3. A minimum periodicity of transmitting the SIB1 is usually large (e.g., 640 ms), and the legacy UE can only change the UL/DL configuration with the periodicity equal or greater than 640 ms. The semi-statics allocation cannot match fast varying traffic characteristics and environments, and there is space for improving system performance. Thus, changing the UL/DL configuration with a lower periodicity (e.g., lower than 640 ms) is considered.
In general, the legacy UE is configured with a UL/DL configuration according to the SIB1, and this UL/DL configuration is also known by an advanced UE which is configured with an additional UL/DL configuration. The additional configuration is a real configuration operated by the eNB, and the eNB provides services (i.e., performs transmissions and/or receptions) to both the legacy UE and the advanced UE according to the additional configuration.
However, when the legacy UE and the advanced UE are configured with difference UL/DL configurations, a collision of HARQ resources may occur if the legacy UE and the advanced UE intend to transmit HARQ feedbacks in a same UL subframe. The collision may occur due to that the legacy UE and the advanced UE transmitting the HARQ feedbacks by using overlapped HARQ resource (e.g., the same HARQ resource) in the UL subframe. In this situation, the network cannot detect the HARQ feedbacks transmitted by the legacy UE and the advanced UE. Communications between the network and the legacy UE and the advanced UE cannot proceed regularly.
Thus, how to solve the collision of the HARQ resources caused due to different UL/DL configurations of the legacy UE and the advanced UE is an important topic to be discussed.